Electrophotographic imaging and copying process



Nov. 4, 1969 MASAMICHI SATO ETAL 3,

ELECTROPHOTOGRAPHIC IMAGING AND COPYING PROCESS Filed July 21, 1966INVENTORS.

' MASAMICHI SATO SATORU HONJO MASAAKI TAKIMOTO ATTORN EYS.

United States Patent Us. Cl. 204-18 19 Claims ABSTRACT OF THE DISCLOSUREA recording method involving electrolytic deposition of material on aphotoconductive element including providing a low adhesion layer on thesurface of a photoconductive element, electrolytically depositing thematerial on the low adhesion layer of the photoconductive element, afterexposure, and then transferring the deposited material from the lowadhesion surface to the surface of a record receiving element.

This invention is concerned with an improvement in electrolyticdevelopment applicable to photography, reproduction, printingfacsimiles, etc. and other such processes utilizing electrolysis.

\ For convenience of illustration there will now be described a methodfor the reproduction of images by subjecting a photoconductive layer toelectrolysis while the photoconductive after-effect remains,afterexposure to light or at exposure to light, thereby selectivelydepositing a material on the exposed portion in accordance with theextent of exposure. In practicing such method, a uniform mixture of aphotoconductive zinc oxide and insulating resin is applied to a baseplate having a high electric conductivity. After dark adaptation, thecoated plate is subjected to image exposure, usually negative imageexposure, and the plate is immediately subjected to electrolysis in anaqueous solution containing a dye forming ionic material, such asquaternary anhydro base, nickel chloride or silver nitrate, while usingthe zinc oxide layer as a cathode. Since the conductivity on the exposedportionrer'nains, even after the cut-off of light, a large quantity'ofelectric current is passed through the exposed por- 3,476,659 PatentedNov. 4,, 1969 lCC and contraction in response to changes in temperatureand humidity, such as polyethylene terephthalate, should be employed,since the expansion and contraction during the treatment are notfavorable. This increases the cost for a support and limits its wide useas a printing material. A metal plate may be employed as a support, of

- course, but it is limited to a peculiar use.

tion, during the electrolysis, to form silver or nickel. The

dye also deposits with the passage of electric current. (Cf. Japanesepatent publications No. 6669/1959 and No. 11544/1964.)

When it' is subjected to exposure and development three times by using acolor negative as an original and filters of three primary colors incombination, a color positive can be obtained.

' Moreover, it is possible to provide an original for offset printing byutilizing the change of pH at electrodes u'pon electrolysis, forexample, to deposit a colorless metal hydroxide.

The method as described above can always be effected onlyifa'p'hotoconductive layer is used having a photoconductive after-effect,but it will be understood that various difficulties may be encounteredin the practice thereof on a commercial basis.

Above all, the important problems are as follows:

(1) A paper or plastic film having a thin metal layer provided by vapordeposition or lamination, used as a base plate or suppo'rt, is hard tohandle as compared with usual papers, since'the metal layer tends to beinjured.

- (2) Aluminum has been found to be suitable for use as a thin metallayer in such elements, but in any case the surface condition on which alight sensitive layer is to be provided has a remarkable influence uponthe finished image. That is, if the surface of a metal layer is coarse,a similarly coarse pattern appears in the image formed by electrolysis.Therefore, the finishing of the surface should be carried out with greatcare, which further increases the importance of the first abovedescribed disadvantage.

' (3) Unless the coating of a photoconductive layer is carried out withgreat care, a number of pinholes are formed in the coating structure anda reduced metal deposits on these portions, which results inshortcircuits and retards image formation on other portions. An increasein the amount of the binder (insulating resin) is effective to make thephotoconductive layer mechanically strong, but on the other hand,hinders the contact of the photoconductive material itself and tends tolower light sensitivity to a great extent.

(4) In color reproduction, it is desirable that the light sensitivelayer have a light sensitivity over the whole range of wave lengths ofvisible rays. If so, the appearance of the light sensitive layer isnaturally gray to black or at least is not pure white. Although anyspectral characteristic is permitted, if three resolving negatives arespecially provided, such complicated procedure is now out of thequestion. If the back-ground is of pure white, it is done at thesacrifice of the light sensitivity to maintain the appearance nearlywhite. For example, in using zinc oxide as a photoconductive material,two or three sensitizing dyes are added so as to impart the panchromaticproperty thereto, since the intrinsic absorption range of zinc oxide isin the near ultraviolet portion. In this case, the amount of the dyes ismaintained as low as possible because of the reason mentioned above.Thus, possible increase of light sensitivity is hereby given up and theutilization of colored photoconductive material is similiarlyrestricted.

(5) A photoconductive layer containing zinc oxide, being chemicallyactive and having photocatalytic action under radiation of light, tendsto decompose organic compounds. Therefore, images formed thereon byelectrolysis discolor in the course of long storage, and this isaccelerated by zinc oxide.

We have made efforts in order to solve a number of problems as describedabove and succeeded therein by the following novel method: Aphotoconductive layer is so composed that at least its surface is of lowadhesiveness and an electrolytic product formed by electrolysis can bereadily stripped from the photoconductive layer, so that the imageconsisting of the electrolytic product is transferred to a recordreceiving element. This transfer should be substantially complete tosuch an extent that the photoconductive layer can be reused after thetransfer. If this is done, the light sensitive material can be usedrepeatedly. The cost per one print can be overlooked, even if the costrequired for the production of the light sensitive material is high. Theforegoing problems (1) and (2) can be solved by a single effort. It willbe understood that problems 4) and (5) are also solved. Moreover, it isfound that the remaining problem (3) is somewhat improved by thepresence of the surface layer of our invention.

, In a color reproduction, if an image is transferred to a suitablesurface, after exposure and development three times, the cost requiredfor a material of the finished print is reduced remarkably, because itdoes not matter whether that surface is of a material which isexpansible and contractible. In addition, the light sensitive layer,after the transfer, is returned to a state suitable for reuse.

The structure of the light sensitive material of our invention is shownin the accompanying drawing, wherein 1 is a support, such as, paper,plastic film and a metal plate, 2 is an electrically conducting layersuch as an aluminum vapor deposition layer or high conductive metalfilm, a subbing layer is provided between 1 and 2 for the purpose ofstrengthening the adhesion thereof as occasion demands, 3 is aphotoconductive insulating layer, for example consisting of a uniformmixture of zinc oxide and a binder and 4 is a thin low-adhesion layer,the surface of which, for example, consists of a silicone-type surfacereleasing agent. In this layer, if necessary, may be incorporated amaterial miscible with a silicone type surface releasing agent, such as,nitro-cellulose, polyvinyl acetate, carboxymethyl cellulose, andpolyvinyl alcohol.

Silicone oils and waxes may be used for the low adhesive layer inaccordance with the use. The surface layer is not present as a clear,independent layer, but may be uniformly mingled with a photoconductivelayer so as to give a low adhesion surface. Of course, the whole body ofa light sensitive material may be so composed. The important point liesin that the surface has a low adhesiveness.

The low adhesion surface means a surface having a low alfinity to anumber of strongly viscous and adhesive materials, even if pressedstrongly against each other, and a good stripping property therefrom. Ithas been well known that paraffin-type compounds exhibit lowadhesiveness. Therefore, polyethylene has such property. Fluorine resinshave the same property. A layer consisting of a silicone type surfacereleasing agent that has been marketed of late exhibits more excellentproperties than those described above or has no affinity to very viscousand adhesive materials. The characteristic of the low adhesion layer isrepresented by the force required to strip a strongly viscous andadhesive material, to be the standard, from the layer onto which theadhesive material is pressed in a predetermined manner. In the presentinvention, the force required for stripping a strongly adhesive tapepressed at a rate of about 30 cm./min. onto the low adhesion layer ispreferably 100 g./cm. or less. Of course, the lower is the requiredforce the better is the low adhesion layer.

Silicone type surface releasing agents are on the market in forms ofaqueous emulsions and organic solvent solutions and it is found that anyof them may be employed in our invention. In particular, the use of theformer raises no fear of attacking the photoconductive layer,

because the photoconductive layer often uses a binder miscible withorganic solvents and immiscible with water. However, there may bedisadvantage in that the coated surface is not uniformly wetted. In thecase of using an organic solvent solution, on the other hand, a uniformthin layer is readily formed but the binder in a photoconductive layeris often dissolved therein. In such cases a special coating procedureshould be devised.

The thickness of the surface layer, if it covers the whole surface,should be as thin as possible. A thick layer hinders the passage ofelectric current, resulting in reduction of the practical sensitivityand operating speed in our invention. It has been made clear by ourexperiments that the electrolysis takes place without trouble at athickness up to several microns, a preferred range being less than 2microns.

In the present invention, furthermore, the decrease of pinholes isobserved as an unexpected merit. This merit will enhance thegreatimprovement of our invention,

because we airn to use a photoconductive layer as many times aspossible.

The invention will be further illustrated by the following examples.

Example 1 parts of photoconductive zinc oxide, 25 parts of a copolymerof styrene and butadiene Pliolite S-7 (manufactured by Goodyear Tire &Rubber Co.) and 75 parts of toluene were charged to a ball mill ofporcelain and mixed for a long time to give a uniform dispersion.

The thus treated cylinder was allowed to stand in a furnace at C. for 20minutes to cure the surface layer thereof.

This light sensitive material, after standing in a dark place for 1hour, was exposed through a negative image and immediately developed bythe following electrolytic developing solution:

Parts Silver nitrate 1 Thiourea 1.35 Acetamide 4 Water to 100 parts.

In the electrolysis, the zinc oxide layer was used as cathode and adirect current of 4 v. was applied. A silver image was obtained as apositive image. After drying, the image was transferred completely to amarketed cellulose tape by pressing it lightly to the surface of thephotoconductive layer. Thirty different images could be obtained fromthe same photoconductive layer by repeating the similar steps whilebringing the light sensitive material into a dark adaptation state.There was little difference in the image quality of the first image andthirtieth image, and the light sensitive layer could be used more.

It is evident from the foregoing experiments that the surface layer hasno influence upon the passage of electrolytic current in spite of thefact that it is of an insulating material. The adhesion of the lowadhesion layer and photoconductive layer is good enough to resist torepeated uses. The generation of pinholes was not observed before thetenth treatment. The good adhesion of the low adhesive layer and thephotoconductive layer is likely due to the fact that there is noelfective force between the photoconductive layer and the low adhesivelayer, since an adhesive tape has no affinity to the low adhesion layer.It is natural that the formation of pinholes can be suppressed byperforming the stripping of an adhesive tape with great care. When aportion free of -a low adhesive layer is subjected to the similar tapetreatment for comparison, a part of the image and photoconductive layerwas transferred to the side of the tape and it could not be reused.Furthermore, another method comprising using a thermoplastic film inplace of the adhesive tape and transferring an image with heating, afterplacing it upon the image, was favorably carried out. In general, athermoplastic film is superior to an adhesive tape, since the adhesivelayer of the latter contains often a plasticizer or solvent for dyes,whereby an image is blotted in the course of a long storage.

Example -2 The following dyes were added to the mixture of Example 1 fordye-sensitization to impart a light sensitivity over the. whole visiblerange and. applied to thesame support as in Example 1, followed bydrying.

Q A NEOaSQC OIOl'part or parts 'ofZnO p To the thus formed lightsensitive layer was applied, by spraying, a silicone surface releasingagent having following composition:

Parts Shin-Etsu Silicone KS-705 (non-volatile matters Catalyst for theforegoing 0.6 Glacial acetic acid 0.05 Toluene 82 The coating was thenheated at 150 C. to cure cornpletely. The light sensitive layer wasbrought into a dark adaptation state and subjected to exposure threetimes by the use of a color negative as an original and a red, blue andgreen filter. After exposure through the red filter, it was subjected toelectrolytic development using a cyan dye. Similarly, a yellow dye wasused for the blue filter exposure and a magenta dye for the green filterexposure. As the cyan dye, Alcian-Blue8GN was used. Yellow thiuroniumcompound obtained by reacting bis(chloromethyl)-4,4-bis(6-methylbenzthiazyl-2-)-azobenzene and N,N,N',N'-tetramethylthiourea was used as the yellow dye, and thiuronium saltof Anthragen Red Violet RHC obtained by the reaction thereof withN,N,N',N'-tetramethylthiourea, as the magenta dye. The methods for thesynthesis of these dyes are described in Japanese patent publication No.15,444/1963.

When the image obtained on the light sensitive layer was rubbed withfingers, it was easily taken off. After drying the light sensitivelayer, a Baryta paper coated with gelatin was moistened a little withwater and pressed thereto, whereby the color image was transferredsubstantially completely. The light residual image could be readilyremoved by applying a strong stream of water thereto and the lightsensitive layer was thereby returned to a state ready for reuse.

It will be understood from the above description that a novelphotographic process having the following advantages is made possible inaccordance with the invention:

(1) Any support can be adapted therefor.

(2) Any light sensitive layer can be used, because its color tone andmechanical properties have no influence upon the final prints.

(3) Restrictions in respect of a cost for a light sensitive material canbe relaxed to a great extent, because the light sensitive layer isresistant to repeated uses.

I (4) Formation of pinholes in the light sensitive layer duringelectrolysis is decreased. I

(5) The contrast and the density of an image transferred can becontrolled. For example, when a sufficient density of an image is notobtained by one electrolytic development, the image is once transferred,and the same image is put on after the second exposure and development.The control of contrasts will be performed similarly.

The present invention is applicable to other recording methodsaccompanied by electrolysis. One of them, for example, comprisesproviding a material consisting of an electrically conductive thin layercovered with an insulating coating, breaking the insulating coating bymeans of a pen pressure or discharge in accordance with an image,subjecting this, as a master, to electrolysis in a suitable electrolyticbath, whereby to deposit a metal, dye or metal hydroxide on theconductive portions from the electrolytic bath, and transferring thethus deposited material to a transfer material by suitable means. Anumber of reproductions are thereby obtained, but it is very importantin this method also that the transfer is satisfactorily carried out. Inorder to apply the present invention to such case, the followingprocedure is preferred. A master obtained once by suitable means iscoated thinly and uniformly with a silicone oil, fluorinated hydrocarbonoil or silicone surface releasing agent. The resulting layer acts as asurface releasing agent without hindering of the passage of electriccurrendt, resulting in a similarly remarkable improvement.

Example 3 As the surface releasing agent of Example 2 required much timefor curing, a solution of polymethylsiloxane having a viscosity of cp.at normal temperature in toluene was applied to an original plate byspraying in place of the surface releasing agent of Example 2. Thismethod appeared to be similarly effective for our aims.

An electrically conductive pattern than can be adapted for electrolyticdevelopment may be obtained by many other methods. For example, in usinga light sensitive layer whose electric resistance is remarkably loweredby applying pressure thereto or a recording material comprising anelectrically conductive thin layer continuously provided with such apressure sensitive layer, that is, to be transferred to some othersupport by pressure, a master will be readily obtained by a penpressure.

When the present invention is applied to those methods in combination,images obtained by electrolysis are readily transferred to othertransfer materials to thereby give a plurality of prints.

A permanent electrically conductive pattern may be obtained by providinga photoconductive layer utilizing a photoconductive material to bereduced electrolytically, for example, zinc oxide and/ or indium oxideand subjecting the photoconductive layer to electrolysis in aqueoussolution of alkali metal halide, whereby to reduce the compounds in thephotoconductive layer.

A still further application of our invention consists in makingfacsimiles. Our invention gives records not accompanied bydiscolorations or changes in color with the passage of time in a methodwherein electric signals transmitted in accordance with informationmodulate the voltage of a needle-like electrode to color an electriccurrent color forming paper. For example, when a low adhesion layer isapplied thinly to the surface of a metal drum, an electrolytic colorforming solution is flowed thereon and the recording is carried out by aneedle-like electrode, dyes and other electrolytic products aredeposited on the low adhesion layer once. The drum is then immersed inwater with revolving to wash electrically conductive salts and colorforming components off, and

7 subjected to transferring to a suitable support. The drum can bereused, if necessary, by washing with water again.

The present invention, as is evident from the above descriptions, willbe applied to all technical fields utilizing electrolysis, such aselectrolytic electrophotography, printing, printed circuits andfacsimile.

What is claimed is; 1. A recording method involving electrolyticdeposition of material on a photoconductive element which comprisesproviding a low adhesion layer on the surfac'e'of said photoconductiveelement, electrolytically depositing a material on the low adhesionlayer of the photoconductive element, after exposure, and thentransferring the deposited material from the low adhesion surface to thesurface of a record receiving element. A

2. The method of claim 1 further comprising restoring thephotoconductive element to a condition ready for reuse.

3. The recording method according to claim 1 wherein, said low adhesionlayer comprises a silicone surface releasing agent.

4. The recording method according to claim 1 wherein said electrolyticdeposition is conducted in an electrolyte containing a silver salt and asilver image is formed on the low adhesion layer and is then transferredto the surface of the record receiving element.

5. The recording method according to claim 1 wherein the photoconductivelayer of said photoconductive element contains at least one dyesubjected to dye sensitization and said electrolytic deposition isconducted in an electrolyte containing at least one dye to deposit acolor image on the low adhesion layer.

6. A recording element for electrolytic recording comprising anelectroconductive layer, operative as an electrode during theelectrolysis and a photoconductive layer,

8 coated on said electroconductive layer said photoconductive layerhaving a low"adhesion"s'urface.

7. The recording elementaccording to claim 6 wherein said low adhesionsurface comprises a silicon surface releasing agent.

8. The recording element according to claim 6 wherein saidelectroconductive support is aluminum and said photoconductive layercomprises zinc oxide.

9. The recording element according to claim 8 wherein said support isselected from the group consisting of paper and plastic film, saidelectroconductive layer is aluminum, said photoconductive layercomprises zinc oxide and said low adhesion layer comprises a siliconesurface releasing agent. r

10. A recording element for electrolytic recording comprising a support,an electroconductive layer, operative as an electrode during theelectrolysis, on said support, a photoconductive layer on saidelectroconductive layer and a low adhesion layer on said photoconductivelayer.

References Cited UNITED STATES PATENTS 3,165,458 1/1965 Harriman 204-183,242,858 3/1966 Eastman et al. 204-18 3,363,556 1/1968 Shely et al.101-469 v I FOREIGN. PATENTS 1,006,115 9/1965 Great Britain.

JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner C l. XR. Y 101469

